<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>可选链操作符</title>
</head>
<body>
  <script>
    //?.
    function main(config){
      // const dbHost = config && config.db && config.db.host
      const dbHost = config?.db?.host;
      console.log(dbHost);
    }

    main({
      db:{
        host:'192.168.1.100',
        username:'root',
      },
      cache:{
        host:'192.168.1.200',
        username:'admin'
      }
    })
  </script>
</body>
</html>